The Impact of Biomass Burning on Cloud Optical Properties

The impact of aerosols on the Earth's radiation budget is not well understood. The direct scattering and absorption of solar radiation by aerosols can result in a cooling or warming effect on the global climate, respectively. The indirect effect of aerosols is related to their ability to act as cloud condensation nuclei (CCN). Previous studies have shown that the available atmospheric water vapor can be distributed over a much larger number of pollution aerosols resulting in smaller cloud droplets and therefore whiter clouds in areas downwind from large cities and wildfires. As a result of the altered cloud optical properties, more incoming solar radiation is reflected rather than being able to penetrate through to the surface, causing an overall cooling effect. For this study, fire radiative power (FRP) data for the western United States was retrieved from USDA Forest Service to identify days with and without significant fire activity. MODIS aerosol optical depth (AOD), cloud optical depth (COD), and cloud top height were used to conduct statistical analysis on the optical properties of clouds of days influenced by the aerosols from biomass burning versus days that were not affected. The cloud optical depths of several cloud types were recorded and compared in order to observe any trend between clouds influenced by aerosols emitted from wildfires versus ones that had not.